Quality control in sawmills is becoming increasing important. Lumber graders are hired to examine lumber travelling on sawmill conveyors to separate high quality lumber from lower quality grades. In order to grade individual lumber pieces, the graders frequently need to turn the lumber pieces. Over time this may result in repetitive motion injuries such as carpo tunnel syndrome. Also, manually turning lumber boards is time consuming and can distract the operator from the primary task of grading the lumber.
Some mechanical lumber board turners are know in the prior art to address this problem. Shark Fin™ board turners available from Redco Group are capable of turning boards individually. However, such prior art board turners require modification to the conveyor chain itself (i.e. the mounting of pins or other actuators on the chain for engaging the boards). The use of pin actuators takes up space on the conveyor, limits conveyor speed and may require the use of a singulator to place the boards on the conveyor chain in the required orientation. Moreover, such systems are capable of rotating the boards in one direction only.
Devices are known in the patent literature for turning workpieces travelling on a conveyor. U.S. Pat. No. 4,798,278, Cornacchia, dated Jan. 17, 1989 discloses a conveyor for turning packages upside down in a very gentle manner which eliminates the need for any mechanism which grips the package in order to turn it. However, the Cornacchia device is not adapted for engaging an end portion of the workpiece or for optionally allowing the workpiece to travel through the device.
U.S. Pat. No. 5,482,140, Moore, dated Jan. 9, 1996 relates to a rotary board inverter which relies on the motive force of the boards themselves to invert the boards. The inverter is mounted directly on the conveyor and does not include any means for skipping inversion of selected boards.
U.S. Pat. No. 5,836,438, Jung, dated Nov. 17, 1998 and U.S. Pat. No. 6,142,287, Biffert et al., dated Nov. 7, 2000 disclose other means for inverting, diverting or skipping workpieces travelling on a conveyor. The Biffert et al. includes a servo motor connectable to electronic control circuitry for rotating a pivot shaft. The Jung and Biffert et al. devices are relatively complex and are not adapted for engaging an end portion of a travelling workpiece.
The need has therefore arisen for an improved workpiece turning apparatus which overcomes the limitations of the prior art.